CO₂ reacts with calcium silicate hydrates to form calcite — permanently stored, strength improved.
Concrete curing with CO₂ — also called mineral carbonation or CO₂ curing — is a process where freshly cast concrete products are exposed to a concentrated CO₂ atmosphere during the curing period. The CO₂ reacts with calcium silicate hydrate (CSH) phases in the cement paste to form stable calcite (CaCO₃) and amorphous silica (SiO₂). This carbonation reaction is the same reaction that causes ordinary concrete to slowly absorb CO₂ from the atmosphere over decades — CO₂ curing simply accelerates and concentrates the process using captured CO₂ in a controlled chamber.
The carbonation reaction permanently incorporates the CO₂ into the concrete matrix as a stable mineral solid — the CO₂ does not re-emit during the concrete product's service life (typically 50–100 years) or during demolition and recycling. CO₂ uptake per tonne of concrete ranges from 15–50 kg CO₂/tonne depending on cement content, CO₂ concentration, curing time, and temperature. In addition to CO₂ storage, CO₂ curing improves concrete compressive strength by 10–30% — meaning either stronger concrete at the same cement content, or equivalent strength with reduced cement content (and therefore reduced production emissions).
Beyond CO₂ curing of fresh concrete, two related pathways offer additional CO₂ utilisation: CO₂-mineralised aggregate production, where reactive minerals (steel slag, fly ash, concrete demolition waste) are reacted with CO₂ to produce dense, stable aggregate for concrete and road base; and CO₂ injection into fresh concrete mix (Carbicrete technology), where CO₂ is injected into the concrete batching process rather than in a curing chamber — enabling in-situ carbonation without dedicated curing infrastructure.
CO₂ uptake per tonne of concrete products in CO₂ curing — permanent mineralisation
Compressive strength improvement achievable with CO₂ curing vs. steam curing
India's annual cement production — creating massive CO₂ utilisation capacity in construction
Typical concrete service life — CO₂ stored permanently for the structure's entire lifecycle
Each application has different CO₂ uptake volumes, capital requirements, and market demand profiles.
Precast products — pipes, blocks, pavers, panels, railway sleepers — are manufactured in controlled environments ideal for CO₂ curing chambers. Highest CO₂ uptake per tonne. Several Indian precast manufacturers in Gujarat, Maharashtra, and AP are immediate deployment candidates.
CO₂ injected into the concrete mixer truck or batching plant — no dedicated curing chamber required. CarbonCure Technologies (Canada) system. Most scalable deployment pathway for India's 5,000+ ready-mix plants. Lower CO₂ uptake per batch but massive volume potential.
Steel slag, fly ash, and demolition concrete waste reacted with CO₂ to produce dense, stable aggregate. India produces 20 MT/year of steel slag — most landfilled. CO₂-mineralised slag aggregate replaces quarried stone, simultaneously solving a waste problem and creating a CO₂ utilisation pathway.
AAC — lightweight aerated concrete blocks widely used in Indian housing — is produced in autoclaves that can be retrofitted for CO₂ injection. Large AAC manufacturers in Rajasthan, UP, and Maharashtra are prime candidates for CO₂ utilisation offtake agreements.
Roads, bridges, dams, and railway infrastructure — India's ₹111 trillion National Infrastructure Pipeline — represent the largest potential demand for CO₂-cured concrete. NCM is developing a policy brief for MoRTH and the National Highways Authority to include CO₂-cured concrete specifications in infrastructure procurement standards.
India is currently the world's second-largest construction market by volume and is projected to become the largest by 2030. The National Infrastructure Pipeline (NIP) — a ₹111 trillion (approximately USD 1.4 trillion) programme covering roads, railways, urban infrastructure, housing, and energy — will consume vast quantities of concrete, precast products, and aggregate between now and 2030. The CO₂ utilisation potential embedded in this construction programme is extraordinary: if 10% of India's concrete production incorporated CO₂ curing, the total CO₂ utilised would exceed 30 MT/year — more than the total capture volume of most national CCUS programmes.
The economics of CO₂ building materials in India are favourable compared to most other markets. The primary cost of CO₂ curing is the CO₂ itself — at USD 30–50/tonne (the cost of capture and compression from an industrial source), the CO₂ cost per tonne of concrete product is approximately USD 1.5–2.50. This cost is more than offset by the strength improvement (equivalent to using 10–15% less cement, saving USD 3–5 per tonne of concrete product) and by the carbon credit revenue from the permanently stored CO₂ (at India Carbon Market prices of USD 10–20/tonne CO₂ — this is a further USD 0.15–1.00 per tonne of concrete). CO₂ curing is therefore potentially cost-negative — it reduces concrete production cost while storing CO₂.
NCM is developing a consortium model for CO₂ utilisation in India's construction sector — aggregating CO₂ demand from multiple precast and ready-mix concrete plants in an industrial cluster to create sufficient volume for a shared CO₂ supply pipeline from a nearby capture source. This model — with the Gujarat cement cluster as the first target — reduces the infrastructure cost per tonne of CO₂ utilised and creates a supply agreement structure that carbon project developers and DFI lenders can finance.
NCM's building materials advisory is structured around the supply-demand matching challenge — identifying the CO₂ source (capture plant), the CO₂ transport pathway (pipeline or tanker), the utilisation technology (CarbonCure in-situ injection, purpose-built curing chambers, or mineralised aggregate reactors), and the concrete product offtaker (precast manufacturer, ready-mix company, AAC producer). Each link in this chain requires separate commercial agreements, technical integration, and carbon accounting documentation.
Technology selection depends critically on the scale and flexibility requirements of each deployment. CarbonCure's in-situ injection technology — which injects CO₂ directly into the mixing truck at the batching plant — is the most scalable and lowest-capital option for India's fragmented ready-mix sector, where plant sizes typically range from 10,000–100,000 m³/year. Purpose-built CO₂ curing chambers are better suited to large precast manufacturers (railway sleeper producers, pipe manufacturers, large panel producers) where capital investment is justified by throughput volume and where the 30% strength improvement creates the largest cost saving per tonne of product.
NCM also leads the policy engagement required to create public sector demand for CO₂-cured concrete — because India's construction sector is dominated by public procurement through NHAI, MoRTH, Indian Railways, and state PWDs. Including CO₂-cured concrete in these agencies' material specifications and procurement requirements creates the market certainty that private sector concrete producers need to invest in CO₂ curing infrastructure. NCM is developing the technical standards and procurement specification language for this policy intervention.
Whether you are a government body seeking policy advice, an industrial company facing CBAM exposure, or an investor seeking CCUS project opportunities — our team is ready to engage.